This application is part of a clustered proposal consisting of three components: an application by Dr. Frank Marcus describing the overall scientific program, an application by Dr. Jeffrey Towbin describing the genetic analyses for the study, and a proposal by Dr. Wojciech Zareba describing the organization and operation of the Coordination and Data Center (CDC) for the study. The proposed five-year research plan is a multi-disciplinary, multicenter, collaborative study to investigate the cardiac, clinical, and genetic aspects of arrhythmogenic right ventricular dysplasia (ARVD), a progressive disorder that predominantly affects the right side of the heart and causes ventricular arrhythmias. In many patients the disease is familial. ARVD may account for as many as 5% of unexpected sudden deaths under the age of 65 and 3-4% of sudden death during sports. There can be considerable difficulty in diagnosing this disease with certainty, and there is incomplete information on the pathogenesis, natural history, and treatment of the patients and affected members. The overall objective of the Multidisciplinary Study of Right Ventricular Dysplasia is to characterize the genetic and clinical features of arrhythmogenic right ventricular dysplasia (ARVD). The specific aims are: 1) to establish a North American ARVD Registry enrolling ARVD patients and their family members, based on standardized diagnostic test criteria, in a prospective longitudinal follow-up study; 2) to determine the genetic background of ARVD by identifying chromosomal loci and specific gene mutations associated with this disorder; 3) to determine the influence of the genotype on the clinical course of patients with ARVD and explore phenotype-genotype associations that will contribute to improved diagnosis, risk stratification, and therapy; and 4) to develop quantitative methods to assess right ventricular function in order to enhance the specificity and sensitivity of ARVD diagnosis. This integrated research grant proposal offers a substantial prospect of expanding the fund of clinical knowledge regarding ARVD and of localizing the gene(s) responsible for this disorder.